A tin oxide refractory prepared by sintering a refractory composition containing tin oxide (SnO2) as the main component, has very high erosion resistance to glass, as compared with a refractory which is commonly used, and its use as a refractory for a glass melting furnace is being studied.
For example, Patent Document 1 has proposed a tin oxide refractory for a glass melting furnace containing from 85 to 99 wt % of SnO2. However, no case has been known in which such a refractory is practically used as a refractory for a portion in contact with glass in a glass production apparatus.
The reason is that as a basic characteristic, SnO2 has such a nature that it volatilizes as SnO in a high temperature zone, particularly in a high temperature zone of at least 1,200° C. Such volatilization is considered to bring about such a problem that the surface structure of the refractory tends to be porous and brittle, and SnO2 itself tends to peel off, or a volatilized SnO component tends to be concentrated and coagulated in a low temperature zone in the glass melting apparatus, so that a SnO2 component will fall and be included as a foreign matter in glass, thus leading to deterioration of the yield in the production of a molded product of glass.
On the other hand, a SnO2 sintered body is used as an electrode material for glass melting in a high temperature zone. Usually, such a SnO2 electrode material is made of from 90 to 98 mass % of SnO2 and from about 0.1 to 2.0 mass % of a sintering assistant and an agent to reduce electrical resistance and is utilized as a material having both properties of high erosion resistance to molten glass and low electrical resistance sufficient for power distribution. However, such a common SnO2 electrode material tended to gradually volatilize as SnO in a high temperature zone, particularly in a high temperature zone of at least 1,200° C., whereby deterioration was unavoidable.
As a conventional technique to solve the problem of volatilization of SnO2 in a high temperature zone, Non-patent Document 1 has reported on a SnO2 sintered body wherein 0.5 mol % of CoO as a sintering assistant is incorporated to a SnO2 powder and from 0 to 10 mol % of ZrO2 as a volatilization-preventing component is incorporated based on the total content of ZrO2 and SnO2, to prevent volatilization of SnO2.
Further, Patent Document 2 has proposed an electrode material for a glass melting furnace, wherein together with a sintering assistant and an agent to reduce electrical resistance, as a volatilization-preventing agent, a Y component being an oxide such as ZrO2, HfO2, TiO2, Ta2O5 or CeO2 is incorporated in an amount of from 0 to 8 mass % based on the total content of Y and SnO2, to prevent volatilization of SnO2.
These SnO2 sintered bodies containing a volatilization-preventing component have a structure having the volatilization-preventing agent solid-solubilized inside of SnO2 particles, and when SnO2 volatilizes in a high temperature zone, the volatilization-preventing agent solid-solubilized inside of SnO2 particles will be concentrated and will precipitate on the SnO2 particle surface to cover the SnO2 particle surface, whereby it is possible to prevent volatilization of SnO2.